1. Field of the Invention
The present invention relates to a high-frequency oscillator for use in a millimeter-wave integrated circuit, a millimeter-wave radar module or the like, and specifically, to a high-frequency oscillator in which a bias supply circuit of a variable-capacitance element as a component of the high-frequency oscillator is provided with a pre-set variable resistor, and which can tune oscillation characteristics such as an oscillation frequency and a frequency modulation width to a desired state with the pre-set variable resistor, and to a high-frequency transmission-reception apparatus using the high-frequency oscillator.
Further, the invention relates to a radar apparatus comprising the aforementioned high-frequency transmission-reception apparatus, and to a radar-apparatus-equipped vehicle and a radar-apparatus-equipped small boat that are equipped with the radar apparatus.
2. Description of the Related Art
Since before, a high-frequency oscillator which is integrated and used in a millimeter-wave integrated circuit, a millimeter-wave radar module or the like, for example, as shown by a schematic cross section view in FIG. 16 is known. The high-frequency oscillator shown in FIG. 16 is provided with: a waveguide tube 51 whose one end is short-circuited as a short-circuit end 51a and whose other end is opened as an output end 51b; a Gunn diode 52 that is disposed in the tube in midway of the short-circuit end 51a and the output end 51b of the waveguide tube 51, and that generates high-frequency signals; a bias supply circuit 53 for applying a bias voltage to the Gunn diode 52; a varactor diode 55 serving as a variable-capacitance element, which is disposed on a resonator 54 configured by a portion between the short-circuit end 51a of the waveguide tube 51 among the waveguide tube 51 and the part on which the Gunn diode 52 is disposed; and a bias supply circuit 56 for applying a bias voltage to the varactor diode 55.
Until now, the bias supply circuit 56 used in the high-frequency oscillator as described above is provided with, for example, a fixed resistor such as a chip resistor, and a bias voltage applied to the varactor diode 55 was set depending on the resistance value of the fired resistor.
The high-frequency oscillator as an example of the conventional one can generate high-frequency signals of a millimeter-waveband from the Gunn diode 52 by applying a bias voltage from the bias supply circuit 53 to the Gunn diode 52, resonate the high-frequency signals in the resonator 54, and output high-frequency signals of a frequency of, for example, 77 GHz from the output end 51b of the waveguide tube 51. On this occasion, it is possible to change the frequency of output high-frequency signals by changing the capacitance value of the varactor diode 55 disposed on the resonator 54. It is possible to change the capacitance value of varactor diode 55 by a bias voltage applied to the varactor diode 55. That is to say, by controlling a bias voltage outputted from the bias supply circuit 56 and applied to the varactor diode 55, it is possible to control the oscillation frequency of the high-frequency oscillator, and, for example, by providing the bias supply circuit 56 with a modulation signal source that generates voltage signals such as triangular waves as modulation signals, it is possible to cause to output frequency-modulated high-frequency signals from the high-frequency oscillator.
Further, the high-frequency oscillator as the example of the conventional one may use a nonradiative dielectric waveguide (also referred to as an NRD guide hereinafter) as a high-frequency transmission line instead of the waveguide tube 51, and such conventional examples are disclosed in, for example, Japanese Unexamined Patent Publication JP-A 6-268445 (1994), Japanese Unexamined Patent Publication JP-A 6-268446 (1994), Japanese Unexamined Patent Publication JP-A 6-268447 (1994) and Japanese Unexamined Patent Publication JP-A 6-291552 (1994).
The basic configuration of the nonradiative dielectric waveguide is, as shown by a partially cutaway perspective view in FIG. 17, a configuration such that a dielectric line 63 whose cross section shape in one virtual plane perpendicular to a direction in which a line extends, is a rectangular shape such as a rectangle is placed between parallel flat plate conductors 61, 62 placed in parallel at a predetermined space a, and in the case where the relation between the predetermined space a and a wavelength λ of high-frequency signals is a ≦λ/2, it is possible to avoid penetration of noise into the dielectric line 63 from the outside as well as avoid radiation of high-frequency signals to the outside, and make high-frequency signals propagate in the dielectric line 63 with efficiency. The wavelength A of high-frequency signals is a wavelength in the air (free space) at a used frequency.
Furthermore, the conventional high-frequency oscillator is, for example, as disclosed in Japanese Unexamined Patent Publication JP-A-2000-258525, integrated into a high-frequency transmission-reception apparatus that transmits and receives high-frequency signals, and moreover, used in a radar apparatus into which the high-frequency transmission-reception apparatus is integrated. In the high-frequency transmission-reception apparatus or the radar apparatus, the high-frequency oscillator operates so as to generate high-frequency signals of, for example, a millimeter-waveband and output high-frequency signals obtained by subjecting the generated high-frequency signals to frequency-modulation such that the frequency repeatedly ascends and descends between the lower limit value and the upper limit value of the frequency in a specific frequency range. Then, an operation such that the high-frequency signals outputted from the high-frequency oscillator are additionally pulse-modulated by a modulator and outputted as transmission high-frequency signals from an antenna is performed. There is also a case where high-frequency signals outputted from the high-frequency oscillator are outputted as transmission high-frequency signals as they are.
Still further, an example of a conventional radar apparatus and a radar-apparatus-equipped vehicle equipped with the radar apparatus is disclosed in, for example, JP-A-2003-35768.
However, the conventional high-frequency oscillator and the high-frequency oscillators as disclosed in JP-A 6-268445 (1994), JP-A 6-268446 (1994), JP-A 6-268447 (1994) and JP-A 6-291552 (1994) have a problem that subtle differences in connection states and operation states (referred to as load conditions) of the high-frequency transmission line connected to the output end of the high-frequency oscillator and other high-frequency circuit elements easily cause a change of oscillation characteristics such as an oscillation frequency and a frequency modulation width, and therefore, it is hard to stably obtain desired oscillation characteristics. The frequency modulation width means a width in which a frequency is changed in the frequency modulation.
Further, the high-frequency transmission-reception apparatus using the high-frequency oscillator as described above has a problem that at the time of mass-production thereof, load conditions of the high-frequency circuit elements connected to the high-frequency oscillators and load characteristics of the high-frequency oscillators themselves may be individually different, the integrated high-frequency oscillators are hard to have desired oscillation characteristics, and therefore, it is difficult to stably obtain a good transmission-reception performance.
A radar apparatus disclosed in JP-A 2000-258525 also needs to use the high-frequency oscillator as described above, and have same problem as mentioned above.